Integrated three function valve

ABSTRACT

An integrated three function valve (ITFV) that combines the functions of a bypass valve (e.g.  183   a,    185   a,    161   a ) into a single assembly is disclosed. The ITFV allows continued operation after any two failures. With the integrated three function valve, no combination of electrical or hydraulic component failures, regardless of expected failure rate, will prevent an actuator from continued safe operation

TECHNICAL FIELD

[0001] The present invention relates to actuation systems for aircraft.In particular, the present invention relates to fly-by-wire rotoractuation systems for tiltrotor aircraft.

DESCRIPTION OF THE PRIOR ART

[0002] Compared with conventional fixed wing commercial aircraft, thetask of designing helicopter flight control systems to avoid flightcritical failure modes is considerably more challenging. For typicalfixed wing commercial aircraft, flight control system redundancy can beprovided through the application of multiple independently actuatedsurfaces. An example of this methodology is the use of two or threeailerons per wing. Configured in this manner, continued safe flight isachieved in the event of an aileron becoming uncontrollable or seized.

[0003] On the other hand, in helicopters and tiltrotor aircraft,application of multiple independently actuated rotors to provide flightcontrol system redundancy is not a viable option. Typically in rotorsystems, multiple flight control actuators are structurally ormechanically linked together to provide redundancy of actuation. Thismethodology provides for continued safe flight following the failure ofa system or actuator, except for cases where a failed actuator cannot befreely backdriven, or bypassed, by the remaining actuators. For thesefailure modes, the result will be loss of rotor control. Therefore, itis a critical requirement for rotor control actuators that their designsincorporate devices that can reliably ensure that a failed actuator canbe overridden. For hydraulic actuators, this implies ensuring a bypasscondition.

[0004] In conventional fly-by-wire (FBW) rotor control actuation, triplehydraulic redundancy is achieved by employing a dual tandemconfiguration, i.e., two rams end to end. A switching valve is used toconnect two independent hydraulic sources to one of the tandem rams.This ram is controlled by dual redundant electrohydraulic valves anddual redundant signals from a flight control computer (FCC). Typically,the tandem ram configuration is supported with spherical bearings oruniversal joints to minimize structural bending loads.

[0005] Referring to FIG. 1 in the drawings, another type of FBW rotorcontrol system, one having three hydraulic rams arranged side-by-side ina triangular pattern, is illustrated. As is shown in FIG. 1, a rotorcontrol system 10 for the left hand nacelle of a tiltrotor aircraftincludes a triplex collective actuator 11 in which each of three rams13, 15, 17 is hydraulically powered and controlled from one of threeindependent manifolds, hydraulic systems, and FCC's. By using three ramsinstead of two, this configuration has the advantage of eliminating theneed for hydraulic switching valves, control systems, and theirassociated failure modes. Degradation of actuator load/rate capacityfollowing a single failure and the severity of transient motions fromcontrol failures are also improved by having two rams continuing tooperate instead of only one following a single failure.

[0006] Referring now to FIG. 2 in the drawings, each collective actuatorhydraulic manifold comprises an electrohydraulic servo-valve (EHSV) 21,a bypass valve 23 controlled by a solenoid valve 25 to disengage acylinder 27 in the event of a fault, a differential pressure sensor 29to allow force balancing across the triple active cylinders to minimizebending loads (a load control concept used in various configurations onother aircraft), and a pressure relief valve 31 to limit cylinderpressures during adverse failure conditions. For each system, fourlinear variable displacement transducers (LVDT) 33 a, 33 b, 33 c, 33 dare fitted for control and monitoring of the spool of EHSV 21, the spoolof bypass valve 23, the spool of differential pressure sensor 29, and aram piston 35 of cylinder 27, respectively.

[0007] Differential pressure sensor 29 includes spring centered pistons37 with one side ported to extend pressure and the other to retractpressure. The displacement of sensor pistons 37 is measured by LVDT 33 cand is proportional to the delta pressure acting on ram piston 35.

[0008] Although the foregoing designs represent considerableadvancements in the area of rotor control systems, significantshortcomings remain.

SUMMARY OF THE INVENTION

[0009] There is a need for a rotor control system for an aircraft thatprovides full triple redundancy.

[0010] Therefore, it is an object of the present invention to provide arotor control system that provides full triple redundancy.

[0011] This object is achieved by providing an integrated three functionvalve (ITFV) that combines the functions of a bypass valve, a pressurerelief valve, and a differential pressure transducer into a singleassembly. The ITFV of the present invention allows continued operationafter any two failures. With the integrated three function valve of thepresent invention, no combination of two electrical or hydrauliccomponent failures, regardless of expected failure rate, will prevent anactuator from continued safe operation.

[0012] The present invention provides for safe operation of an aircraftby ensuring that electrical and hydraulic component failures do not liedormant in the actuator, such as when a component is not used duringnormal operation, or when a component is not capable of beingperiodically tested. For example, the present invention provides forsafe operation of an aircraft in the presence of the following dormantfailures:

[0013] 1. An EHSV failure, hardover or at null position, in combinationwith failure to bypass the cylinder. The degradation in load ratecapacity resulting from the combination of driving flow across therelief valve on the failed cylinder and increased friction from bendingis not acceptable.

[0014] 2. An EHSV sticking at null position combined with the stickingof the pressure relief valve (PRV), a dormant failure. With this type offailure, acceptable ram pressures can be exceeded. Although thiscondition can be overridden by a bypass valve, it is considered that thetotal time required between failure detection and achieving bypass isnot adequate to protect the failed ram from a spike ofoverpressurization. This condition is a greater problem for the triplexram than for the duplex ram, as the peak load can be three times thedesign stall, i.e., two active rams at stall plus air load; compared totwice the stall, i.e., one active ram at stall plus air load. Therefore,with an aircraft system operating pressure of 21.68 MPa (3,000 psi),this failure combination can generate a pressure spike of 62.05 MPa(9,000 psi). This type of failure on a triple ram system can exceednormal design burst conditions of 1.71 MPa (7,500 psi) burst pressurerequired for 21.68 MPa (3,000 psi) system actuators, unless excessiveweight is added to accommodate the failure mode.

[0015] 3. A loss of two hydraulic or two FCC systems combined with thedormant failure of a PRV. The ram controlled by the one remainingfunctioning system will be required to react all flight loads. If theram on the remaining system contains a PRV that opens at pressures belowsystem operating pressure, control of the actuator can be lost. Apreflight built-in test (PFBIT) can be incorporated into the FCC's toload each ram to stall in order to confirm that the PRV's do not openbelow system pressure. However, this subjects the actuator and structureto severe fatigue loads.

[0016] 4. In the event of the loss of one ram due to FCC or hydraulicsystem failure, the two functioning rams should equally support actuatorflight loads. However, if a failure mode of a delta pressure sensorresults in a pressure indication opposite in direction of the actual ramload, a force fight between the remaining two actuators can result inthe frequency response of the actuator becoming severely degraded. Inaddition to these double failure modes, a change of sensitivity of adifferential pressure sensor can lead to increased fatigue due to anincreased force fight between the triple actuators.

[0017] The present invention provides many significant benefits andadvantages, including: (1) bypass valve function is redundant andindependent; (2) confirmation of redundant bypass valve operation isavailable during PFBIT, and continuous health monitoring is possible incertain applications; (3) PRV function is redundant and independent; (4)confirmation of PRV operation is available during PFBIT, and continuoushealth monitoring is possible in certain applications (5) redundantdelta pressure sensors are provided to permit continuous cross checkingof accuracy; (6) delta pressure sensors are robust and free from commonmode changes in accuracy; and (7) additional actuator redundancy doesnot require any additional wiring or changes to existing FCC interfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIGS. 1A and 1B are perspective views of a prior-art FBW rotorcontrol system having three hydraulic rams arranged side-by-side in atriangular pattern.

[0019]FIG. 2 is a schematic of the collective actuator hydraulicmanifold for the FBW rotor control system of FIG. 1.

[0020]FIGS. 3A-3F are orthographic views of a ITFV collective actuatoraccording to the present invention.

[0021]FIG. 4 is a partial perspective view of a left hand nacelle of atiltrotor aircraft having ITFV's according to the present invention.

[0022]FIGS. 5-12 are schematics of the preferred embodiment of the ITFVaccording to the present shown in various operating states.

[0023]FIG. 13 is a table illustrating ITFV component parameters forbypass time for the present invention.

[0024]FIG. 14 is a table illustrating calculated time to bypass atselected operating temperatures for the present invention.

[0025]FIG. 15 is a table illustrating delta pressure sensor accuracy forthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Referring now to FIGS. 3A-3F in the drawings, the preferredembodiment of an ITFV 111 according to the present invention isillustrated. ITFV 111 utilizes two hydraulic spools to combine thefunctions of bypass valve, pressure relief valve, and delta pressuretransducer into a simple and compact assembly. When used as a matchedpair in a collective actuator, ITFV's 111 provide redundant bypassvalve, pressure relief valve, and delta pressure transducerfunctionality. This allows certain redundancy and monitoringrequirements to be met with fewer springs, hydraulic spools, and pistonsthan other actuator designs.

[0027] Referring now to FIG. 4 in the drawings, three collectiveactuators 113 are shown installed in the left hand nacelle of atiltrotor aircraft. Each collective actuator 113 utilizes a matched pairof ITFV's 111, and is configured to create unequal extend and retractareas to better match predicted flight loads and reduce transienteffects. Flight loads are predominantly in tension. In order to minimizeram bending and associated frictional effects, collective actuators 113are positioned in a plane side-by-side, and are interconnected by arigid bracket 115 on the control surface via spherical bearings 117 oneach collective actuator 113. This configuration and structuralattachment permits ITFV's 111 to fit within the available aircraft spaceenvelope.

[0028] Referring now to FIGS. 5-12 in the drawings, a dual ITFV manifoldassembly 151 having a matched pair of ITFV's 111 a and 111 b accordingto the present invention is shown schematically to illustrate theoperation of the present invention. Although it will be appreciated thatother porting configurations through ITFV's 111 a and 111 b arepossible, the configuration shown in FIGS. 5-12 is particularly wellsuited for use in the tiltrotor aircraft application of the presentinvention. Dual ITFV manifold 151 contains an EHSV 153 with an LVDT 155to monitor spool position. ITFV 111 a is comprised of a pilot spool 157a, a primary spool 159 a, an LVDT 161 a that senses primary spoolposition, and two spool centering springs 163 a and 165 a. ITFV 111 b iscomprised of a pilot spool 157 b, a primary spool 159 b, an LVDT 161 bthat senses primary spool position, and two spool centering springs 163b and 165 b. In the tiltrotor aircraft application used herein, thisconfiguration is possible without requiring any new wiring or FCCinterface changes.

[0029] Two solenoid valves 167 and 169 are utilized to control thebypass function for the pair of ITFV's 111 a and 111 b pair. Solenoidvalve 167 is deenergized “off” to drive the primary spool engagedposition, and solenoid valve 169 is deenergized “on” to control chipshear pressure. The coils of each of the solenoid valves 167 and 169 arewired in parallel. Thus, no FCC or wiring changes are required. Solenoidvalves 167 and 169 are configured this way to achieve a high chip shearcapability, to bypass, when no failures exist, while ensuring thatbypass can be achieved should either solenoid valve 167 or 169 fail todeenergize.

[0030] In FIG. 5, ITFV assembly 151 is shown in a bypass mode, i.e.,solenoid valves 167 and 169 in the “off” position. In the bypass modewith the hydraulic system at operating pressure, system flow is portedto the left side of primary spools 159 a and 159 b, through primaryspool solenoid valve 167, to the pilot solenoid valve 169, and to EHSV153. With solenoid valves 167 and 169 deenergized, primary spools 159 aand 159 b and pilot spools 157 a and 157 b are held in bypass positionby springs 163 a, 163 b, 165 a, and 165 b. Primary spools 159 a and 159b are also held in bypass position by system pressure.

[0031] Primary spool LVDT's 161 a and 161 b provide confirmation to theFCC (not shown) of bypass mode. Flow from a “retract” EHSV control port171 to the retract side 173 of an actuator cylinder 175 is blocked bythe primary spool 159 a. Flow from an “extend” EHSV control port 177 toan extend side 179 of actuator cylinder 175 is blocked by the primaryspool 159 b. This configuration isolates EHSV 153 from actuator cylinder175 in bypass mode, but permits EHSV 153 to be cycled for PFBIT andindependent performance checks. In bypass mode, primary spools 159 a and159 b connect both extend and retract cylinder ports 171 and 177 toreturn and, indirectly, to each other. This allows a shaft 181 ofactuator cylinder 175 to be moved freely by other actuators in bypassmode. Because the unequal area pistons are utilized in ITFV's 111,makeup flow from return prevents cavitation.

[0032] Referring now to FIG. 6 in the drawings, ITFV assembly 151 isshown with EHSV 153 at a null, or center, position with solenoid valves167 and 169 in the engaged “on” mode. With EHSV 153 at null, system flowto the ram ports is blocked by EHSV 153. In the engaged mode with pilotsolenoid valve 169 energized, system flow is ported from pilot solenoidvalve 169 to the right side of pilot spools 157 a and 157 b, drivingpilot spools 157 a and 157 b left to an engaged position. Engagement ofprimary solenoid valve 167 replaces system pressure with return pressureon the left side of primary spools 159 a and 159 b. This allows primaryspools 159 a and 159 b to be centered by the equal preload forces ofsprings 163 a, 165 a, 163 b, and 165 b, respectively.

[0033] LVDT's 161 a and 161 b attached to primary spools 159 a and 159 bprovide confirmation to the FCC that the engaged mode has been achieved.In engaged mode, flow from the retract EHSV control port 171 isconnected through a left side differential area chamber 183 a of primaryspool 159 a to the retract side 173 of actuator cylinder 175. Left sidedifferential area chamber 183 a of primary spool 159 a is also ported toa right side differential area chamber 185 b of primary spool 159 b.Symmetrically, flow from extend EHSV control port 177 is connectedthrough left side differential area chamber 183 b of primary spool 159 bto the extend side 173 of actuator cylinder 175. Left side differentialarea chamber 183 b of primary spool 159 b is also ported to a right sidedifferential area chamber 185 a of primary spool 159 a.

[0034] Left and right side differential area chambers 183 a, 185 a, 183b, and 185 b of primary spools 159 a and 159 b are created by thedifference in diameter between three center lands and smaller end landsof primary spools 159 a and 159 b. The smaller end lands of primaryspools 159 a and 159 b are equal in diameter. Therefore, thedifferential areas on the left and right sides of primary spools 159 aand 159 b are equal. When EHSV 153 is at null, pressures at left andright differential area chambers 183 a, 185 a, 183 b, and 185 b areequal. Therefore, hydraulic forces on primary spools 159 a and 159 b arebalanced, and primary spools 159 a and 159 b remain at the springcentered positions. These positions, as indicated by primary spoolLVDT's 161 a and 161 b, are interpreted by the FCC as zero differentialpressure between extend and retract sides of actuator cylinder 175.

[0035] Referring now to FIG. 7 in the drawings, ITFV assembly 151 isshown engaged with solenoid valves 167 and 169 energized, and with EHSV153 responding to an “extend” computer command from the FCC. EHSV 153directs system flow to extend side 173 of actuator cylinder 175 andconnects retract side 179 of actuator cylinder 175 to return. Pressuregenerated at extend side 173 of actuator cylinder 175 will beproportional to any load restricting actuator movement. Increasingextend side pressure in left side differential area chamber 183 b ofprimary spool 159 b and return pressure in right side differentialchamber 185 b of primary spool 159 b results in a net force thatdisplaces primary spool 159 b to the right, as is indicated by arrow A.Because primary spool 159 b is centered by fixed rate identical springs163 b and 165 b, spool displacement is proportional to the differentialpressure between extend side 173 and retract side 179 of actuatorcylinder 175.

[0036] Displacement of primary spool 159 b resulting from increasedextend pressure causes LVDT 161 b to generate an indication to the FCCof the compression load acting on the actuator. Under increasing extendside pressure, primary spool 159 a reacts identical to primary spool 159b, with the exception of direction of displacement, as indicated byarrow A. Because right side differential area chamber 183 a of primaryspool 159 a is ported to extend pressure and left side differential areachamber 185 a is connected to return pressure, primary spool 159 adisplaces to the left with increasing differential pressure betweenextend side 173 and retract side 179 of actuator cylinder 175.

[0037] Referring now to FIG. 8 in the drawings, the relief valvefunctions of ITFV's 11 a and 111 b will be described. Because ITFV's 111a and 111 b operate in opposite directions, when acting as deltapressure sensors, the possibility of a common mode failure affectingboth sensors accuracy equally is extremely remote. Except for a reversalof the direction of spool displacement and indicated load resulting fromdifferential pressure between extend side 173 and retract side 179 ofactuator cylinder 175, response of primary spools 159 a and 159 b withincreasing retract side cylinder pressure is the same as described forincreasing extend pressure. In the event actuator cylinder 175 issubjected to external loads exceeding acceptable structural limits,primary spools 159 a and 159 b function as relief valves to ventexcessive extend or retract cylinder pressure to return.

[0038] Referring now to FIG. 9 in the drawings, ITFV assembly 151 isshown engaged with solenoid valves 167 and 169 energized, and with EHSV153 in the null position blocking extend port 177 and retract port 171from return or system pressure. When actuator cylinder 175 is subjectedto excessive external compressive load, pressure generated at extendside 173 of actuator cylinder 175 exceeds the relief valve functionopening pressure of 27.58 MPa (4,000 psi). At 27.58 MPa (4,000 psi)extend side pressure, left side differential area chamber 183 b ofprimary spool 159 b generates a net force that displaces primary spool159 b sufficiently to the right to uncover ports and vent excessivepressure to return. Primary spool 159 a reacts identically to primaryspool 159 b, with the exception of the direction of displacement.

[0039] Referring now to FIG. 10 in the drawings, response of primaryspools 159 a and 1-59 b with 27.58 MPa (4,000 psi) retract side cylinderpressure caused by excessive tension load is the same as described for27.58 MPa (4,000 psi) extend pressure, except for a reversal of thedirection of spool displacement resulting from differential pressurebetween extend side 173 and retract side 179 of actuator cylinder 175.Cavitation protection during pressure relief is provided when pairedITFV's 111 a and 111 b are incorporated on unequal area cylinders.Primary spools 159 a and 159 b, venting excessive cylinder pressure inthe same direction as the normal bypass function, connect both cylinderports to return to prevent cavitation. Because the same centeringsprings 163 a, 165 a, 163 b, and 165 b and hydraulic components thatsupport the delta pressure measurement function are also used to providerelief of excessive pressure, the integrity of the ITFV relief valvefunction is continuously monitored in flight.

[0040] When changing from the engaged to the bypass mode, as illustratedin FIGS. 6 and 5, respectively, solenoid valves 167 and 169 aredeenergized. This causes preload in centering springs 163 a, 165 a, 163b, and 165 b to return pilot spools 157 a and 157 b to their disengagedstops. Concurrently, the solenoid valve 167 feeds system pressure, ifavailable, to the left end of both primary spools 159 a and 159 b.System pressure acting on the end areas of primary spools 159 a and 159b generates an 890 N (200 lb) force to move primary spools 159 a and 159b to the right. This force works in combination with preloaded springs163 a, 165 a, 163 b, and 165 b to provide primary spool chip shearcapability when bypass is commanded. This chip shear capability ensuresthat debris that is not filtered by a supply line filter 180 does notprevent movement of primary spools 159 a and 159 b. Filter 180 ispreferably a 100-micron filter.

[0041] For the failure mode where one of primary spools 159 a or 159 bsticks and fails to move into bypass position, the other primary spool159 a or 159 a provides the conditions for bypass. In the event thatsolenoid valve 167 fails to port system pressure to primary spools 159 aand 159 b, the preload of centering springs 163 a, 165 a, 163 b, and 165b is sufficient to move primary spools 159 a and 159 b into bypassposition. For the failure modes where solenoid valve 169 fails to open,or a pilot spool 157 a or 157 b sticks in the engaged position, the 890N (200 lb) force from system pressure acting on the left end of primaryspools 159 a and 159 b is sufficient to compress centering springs 163a, 165 a, 163 b, and 165 b and move pilot spool 157 a and 157 b into thebypass position. Because the same centering springs 163 a, 165 a, 163 b,and 165 b and hydraulic components supporting the delta pressuremeasurement function are also used to provide bypass, the integrity ofthe ITFV bypass function is continuously monitored in flight, with theexception of the solenoid valves.

[0042] Because deenergizing either solenoid valve 167 or 169 will causeboth ITFV's 111 a and 111 b to enter bypass rnode, failure of one ofthese solenoid valves 167 or 169 could lay dormant. To permit the PFBITto identify if either solenoid valves 167 or 169 has failed, ITFVassembly 151 is configured to stop primary spools 159 a and 159 b justshort of the normal bypass position if either solenoid valve 167 or 169has failed. The correspondingly incorrect LVDT output for the bypassposition, provides the FCC with an indication of a failure of eithersolenoid valve 167 or 169.

[0043] Referring now to FIGS. 11 and 12 in the drawings, implementationof this feature is as follows:

[0044] 1. As shown in FIG. 11, in the case where solenoid valve 169 hasfailed, pilot spools 157 a and 157 b remain in the engaged position. Tohalt primary spools 159 a and 159 b just short of the full bypassposition, the right ends of primary spools 159 a and 159 b contact stops186 a and 186 b that extend out from the left ends of pilot spools 157 aand 157 b. System pressure acting on the left end of primary spools 159a and 159 b is sufficient to compress centering springs 163 a, 165 a,163 b, and 165 b, but not enough to move pilot spools 157 a and 157 b.

[0045] 2. As is shown in FIG. 12, in the case where solenoid valve 167has failed, pilot spools 157 a and 157 b move to the disengagedposition. To halt primary spools 159 a and 159 b just short of the fullbypass position, Bellville spring washers 189 a and 189 b are employedon primary spool bypass position stops 187 a and 187 b. The spring rateof washers 189 a and 189 b is sufficient to halt primary spools 159 aand 159 b from achieving a normal bypass position, unless systempressure is supplied through solenoid valve 167 to primary spools 159 aand 159 b.

[0046] Although the present invention combines the three separatefunctions of bypass valve, delta pressure transducer, and PRV into asingle valve assembly, the flexibility to refine components to meetselected performance requirements is not lost. For example, it ispreferred that primary spools 159 a and 159 b fit with very closetolerances in order to minimize internal leakage; however, in order toachieve adequate delta pressure sensor accuracy, a loose spool fit thatminimizes frictional effects is desired. Also, although both leakage andfriction can be reduced by decreasing the ITFV spool diameter, thedesire to have a minimum chip shear force of 890 N (200 lb) duringbypass engagement requires a relatively large spool diameter. Thefollowing is an analysis of how bypass valve response time and deltapressure transducer accuracy can be selectively tailored by utilizingITFV's 111 a and

[0047] Referring now to FIGS. 13 and 14 in the drawings, selectedparameters for bypass time are illustrated in a tables 201 and 301. Theseverity of failure transient actuator motions is directly related tothe speed in which an actuator can be placed into bypass. It ispreferred that ITFV's 111 a and 111 b have a bypass time limit of 30milliseconds. Although the large size of the primary spools 159 a and159 b would make ITFV's 111 a and 111 b slower to respond than smallerdedicated bypass valve spools, because primary spools 159 a and 159 balso function as a delta pressure sensors and PRV's, force fight loadsinduced by EHSV 153 or other failures effectively preposition one ofprimary spools 159 a or 159 b closer to the bypass pass position. Inaddition, full bypass position is not required to disengage the failedactuator cylinder 175. Because the pressure relief ports are uncoveredas primary spools 159 a and 159 b move to the bypass position, any ramforce fight is significantly reduced at that valve position. Thus, thespeed in which the dual ITFV assembly 151 can achieve effective bypassof a failed actuator cylinder 175 under force fight conditions is asfast as, if not faster than, the conventional designs. In FIG. 14, table301 illustrates calculated times for the selected operatingtemperatures. The times listed are all inclusive of solenoid valveswitching time.

[0048] Referring now to FIG. 15 in the drawings, delta pressure sensoraccuracy is illustrated in a table 401. Accuracy of differentialpressure setting is determined by dimensional variations resulting froma combination of manufacturing tolerances, such as LVDT sensitivity,spring rate, spool and sleeve diameters, and differential thermalexpansion. Because the LVDT's 161 a and 161 b are also used to indicatethe bypass positions of primary spools 159 a and 159 b, only 60% of thestroke of LVDT's 161 a and 161 b are used to measure delta pressure.

[0049] Generally, thermal effects influencing delta pressure accuracyare considered as absolute values. It is preferred that the sensor havean absolute accuracy requirement of ±2,068 kPa ([±300 psi]; a worst case±4,137 kPa [±600 psi] between two sensors). However, because the purposeof the delta pressure sensors is to balance ram pressures relative toeach other, it is acceptable to allow greater deviation in the absoluteaccuracy of the sensors, as long as the accuracy of the sensors relativeto each other is maintained. According to a thermal analysis of thehydraulic systems, without failures, the worst case maximum differencebetween the three return system temperatures should never exceed 10° C.(50° F.). Therefore, between actuators, the difference in ITFV deltapressure readings when subjected to fluid temperatures within 10° C.(50° F.) is not allowed to exceed 4,137 kPa (600 psi) up to 20.68 MPa(3,000 psi). This accuracy between lanes falls within a selectedrequirement of 4,137 kPa (600 psi), even given an adverse buildup oftolerances. Allowing for sensitivity variations between LVDT's andmanufacturing tolerances, ITFV lane-to-lane matching within a manifoldis possible to within 13% of reading.

[0050] The integrated three function valve according to the presentinvention is less complex and more reliable than separately housedpressure transducers, bypass valves, and pressure relief valves. Whenused as a matched pair in a hydraulic actuator, ITFV's 111 a and 111 bprovide redundant bypass valve, pressure relief valve, and deltapressure transducer functionality. This added redundancy is achievedwith no additional LVDT's or wiring over conventional arrangements. Thisredundancy allows a control linkage or aerodynamic surface driven bymultiple actuators to continue to operate safely following most commondual failures.

[0051] It is apparent that an invention with significant advantages hasbeen described and illustrated. Although the present invention is shownin a limited number of forms, it is not limited to just these forms, butis amenable to various changes and modifications without departing fromthe spirit thereof.

1. An integrated three function hydraulic valve assembly comprising: amanifold; a primary spool disposed within the manifold; a pilot spooldisposed within the manifold and operably associated with the primaryspool; at least one spring for positioning the primary spool and thepilot spool; and a control system carried by the manifold forcontrolling the primary spool and the pilot spool; wherein the primaryspool and the pilot spool operate to provide a bypass valve function, apressure relief valve function, and a delta pressure transducerfunction.
 2. The hydraulic valve assembly according to claim 1, whereinthe primary spool has at least one differential area chamber.
 3. Thehydraulic valve assembly according to claim 1, wherein the primary spoolhas two opposing differential area chambers.
 4. The hydraulic valveassembly according to claim 1, wherein the control system comprises: anelectrohydraulic servo-valve in fluid communication with both theprimary spool and the pilot spool having a servo-valve spool; at leastone solenoid controlled valve in fluid communication with both theprimary spool and the pilot spool; a first linear variable displacementtransducer operably associated with the primary spool to indicate thelocation of the primary spool; a second linear variable displacementtransducer operably associated with the servo-valve spool to indicatethe location of the servo-valve spool; and a computer conductivelycoupled to the electrohydraulic servo-valve, the solenoid controlledvalve, the first linear variable displacement transducer, and the secondlinear variable displacement transducer for receiving and transmittingoperational instructions thereto.
 5. The hydraulic valve assemblyaccording to claim 1, further comprising: a filter means for filteringdebris from the hydraulic valve assembly.
 6. The hydraulic valveassembly according to claim 1, wherein the bypass valve function, theprqssure relief valve function, and the delta pressure transducerfunction operate independently of each other.
 7. A redundant controlsystem for controlling an hydraulic actuator comprising: a manifold influid communication with the hydraulic actuator; a pair of integratedthree function hydraulic valve assemblies, each hydraulic valve assemblycomprising: a primary spool disposed within the manifold; a pilot spooldisposed within the manifold and operably associated with the primaryspool; a pair of centering springs for positioning the primary spool andthe pilot spool; and a linear variable displacement transducer operablyassociated with the primary spool to indicate the location of theprimary spool; a conduit system disposed within the manifold for placingboth integrated three function hydraulic valve assemblies in fluidcommunication a control system carried by the manifold for controllingthe primary spools and the pilot spools; wherein the primary spools andthe pilot spools operate to provide a redundant bypass valve function, aredundant pressure relief valve function, and a redundant delta pressuretransducer function.
 8. The redundant control system according to claim7, wherein the control system comprises: an electrohydraulic servo-valvein fluid communication with both of the primary spools and both of thepilot spools having a servo-valve spool; two solenoid controlled valvesin fluid communication with both of the primary spools and both of thepilot spools to facilitate the redundant bypass valve means; a firstlinear variable displacement transducer operably associated with thefirst primary spool to indicate the location of the first primary spool;a second linear variable displacement transducer operably associatedwith the second primary spool to indicate the location of the secondprimary spool; a third linear variable displacement transducer operablyassociated with the servo-valve spool to indicate the location of theservo-valve spool; a computer conductively coupled to theelectrohydraulic servo-valve, both of the solenoid controlled valves,and all three of the linear variable displacement transducers forreceiving and transmitting operational instructions thereto.
 9. Theredundant control system according to claim 7, wherein the bypass valvefunction, the pressure relief valve function, and the delta pressuretransducer function operate independently of each other.